Multi-port accumulator for radio-over-fiber (RoF) wireless picocellular systems

ABSTRACT

A multi-port accumulator apparatus for a radio-over-fiber (RoF) wireless picocellular system that includes a housing that supports a tail cable port and a number of RoF transponder ports. The tail cable port is optically coupled to the RoF transponder ports so as to provide for optical transmission of uplink and downlink optical signals between the tail cable port and each of the transponder ports. The tail cable port is also electrically coupled to each transponder port so as to provide electrical power to each of the plurality of transponder ports. The multi-port accumulator supports two or more RoF transponders, one at each RoF transponder port. Each RoF transponder includes a directional antenna system that forms a picocellular coverage sub-area, with the combined sub-areas constituting a picocellular coverage area for the multi-port accumulator. The multi-port accumulator allows for the quick installation and deployment of large numbers of RoF transponders without having to individually connect each RoF transponder to a pair of downlink and uplink optical fibers carried by an optical fiber RF communication link.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to wireless communication systems, and in particular relates to transponders and transponder systems and methods used in optical-fiber-based wireless picocellular systems for radio-over-fiber (RoF) communication.

2. Technical Background

Wireless communication is rapidly growing, with ever-increasing demands for high-speed mobile data communication. As an example, so-called “wireless fidelity” or “WiFi” systems and wireless local area networks (WLANs) are being deployed in many different types of areas (coffee shops, airports, libraries, etc.). Wireless communication systems communicate with wireless devices called “clients,” which must reside within the wireless range or “cell coverage area” in order to communicate with the access point device.

One approach to deploying a wireless communication system involves the use of “picocells,” which are radio-frequency (RF) coverage areas having a radius in the range from about a few meters up to about 20 meters. Because a picocell covers a small area, there are typically only a few users (clients) per picocell. Picocells also allow for selective wireless coverage in small regions that otherwise would have poor signal strength when covered by larger cells created by conventional base stations.

In conventional wireless systems, picocells are created by and centered on a wireless access point device connected to a head-end controller. The wireless access point device includes digital information processing electronics, an RF transmitter/receiver, and an antenna operably connected to the RF transmitter/receiver. The size of a given picocell is determined by the amount of RF power transmitted by the access point device, the receiver sensitivity, antenna gain and the RF environment, as well as by the RF transmitter/receiver sensitivity of the wireless client device. Client devices usually have a fixed RF receiver sensitivity, so that the above-mentioned properties of the access point device mainly determine the picocell size. Combining a number of access point devices connected to the head-end controller creates an array of picocells that cover an area called a “picocellular coverage area.” A closely packed picocellular array provides high per-user data-throughput over the picocellular coverage area.

Prior art wireless systems and networks are wire-based signal distribution systems where the access point devices are treated as separate processing units linked to a central location. This makes the wireless system/network relatively complex and difficult to scale, particularly when many picocells need to cover a large region. Further, the digital information processing performed at the access point devices requires that these devices be activated and controlled by the head-end controller, which further complicates the distribution and use of numerous access point devices to produce a large picocellular coverage area.

Radio-over-Fiber (RoF) wireless picocellular systems utilized optical fibers to transmit the RF signals to RoF transponders that convert the RF optical signals to electrical RF signals and then to wireless electromagnetic (EM) signals, and vice versa. Unlike conventional wireless system access points, the RoF transponders generally do not require any signal processing capability, thereby simplifying the distribution of the RoF transponders to produce a large picocellular coverage area.

While RoF wireless picocellular systems are generally robust, there are some shortcomings. One shortcoming relates to the relative difficulty in manufacturing and deploying an optical fiber cable having a linear array of transponders. Each transponder needs to be optically coupled to an uplink optical fiber and a downlink optical fiber as well as to an electrical power line, usually via a “tether cable.” This involves the tedious and time-consuming process of accessing the uplink and downlink optical fibers and the electrical power line in the cable, splicing the optical fibers and electrical power line, and then connecting them to the transponder. Another shortcoming of the linear array approach for distributing transponders is that the approach is not readily scalable once the system is deployed. This makes it difficult to quickly and inexpensively change the picocell coverage area to accommodate the changing needs or geometry of the particular wireless environment.

SUMMARY OF THE INVENTION

One aspect of the invention is a multi-port accumulator apparatus for operably supporting two or more RoF transponders and for providing a connection to a tail cable that carries uplink and downlink optical signals and electrical power. The apparatus includes a housing and two or more RoF transponder ports supported by the housing, with each RoF transponder port configured to operably connect to one of the RoF transponders. The apparatus also includes a tail cable port supported by the housing and configured to operably connect to the tail cable. The tail cable port is optically and electrically connected to each RoF transponder port so as to provide the uplink and downlink optical signals and the electrical power to each RoF transponder.

Another aspect of the invention is a method of forming a RoF wireless picocellular coverage area. The method includes operably supporting two or more RoF transponders on a housing, and providing downlink optical signals for the RoF transponders to a tail cable port on the housing via a tail cable. The method further includes distributing the downlink optical signals through the housing to one or more of the RoF transponders so that the one or more RoF transponders contribute to forming a picocellular coverage area.

Another aspect of the invention is a multi-port accumulator apparatus for supporting a plurality of RoF transponders for a RoF wireless picocellular system. The apparatus includes a housing, and a plurality of RoF transponder ports supported by the housing. Each RoF transponder port is adapted to operably connect with one of the RoF transponders. The apparatus also includes a tail cable optically coupled within the housing to the plurality of RoF transponder ports so as to provide for optical transmission of uplink and downlink optical signals between the tail cable and the plurality of RoF transponder ports. The tail cable is also electrically coupled within the housing to the plurality of RoF transponder ports so as to provide electrical power to each of the plurality of RoF transponder ports.

Additional features and advantages of the invention are set forth in the detailed description that follows, and will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description that follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description and the following detailed description present embodiments of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the invention and, together with the description, serve to explain the principles and operations of the invention.

Accordingly, various basic electronic circuit elements and signal-conditioning components, such as bias tees, RF filters, amplifiers, power dividers, etc., are not all shown in the Figures for ease of explanation and illustration. The application of such basic electronic circuit elements and components to the systems of the present invention will be apparent to one skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a generalized embodiment of an optical-fiber-based RoF wireless picocellular system showing a single transponder and its associated picocell and picocell coverage area;

FIG. 2 is a detailed schematic diagram of an example embodiment of a head-end unit for the system of FIG. 1;

FIG. 3 is a detailed schematic diagram of an example embodiment of the distribution unit and transponder of the system of FIG. 1;

FIG. 4 is a close-up view of an alternative example embodiment for the transponder shown in FIG. 3 that includes a transmitting antenna element and a receiving antenna element within the transponder housing along with reflectors that enhance the directivity of the antenna elements;

FIG. 5 is a schematic perspective diagram of an example embodiment of a multi-port accumulator according to the present invention that has four transponder ports;

FIG. 6 is a plan view of an example embodiment of the multi-port accumulator of FIG. 5 with the top wall removed, showing the internal uplink and downlink optical fiber sections and the electrical power line sections that connect the tail cable port to the transponder ports;

FIG. 7 is a side view of the multi-port accumulator of FIG. 6 showing the tail cable connected to tail cable port;

FIG. 8 is the same as FIG. 7, but with the sidewall removed to illustrate the optical and electrical connections between the tail cable port and one of the transponder ports;

FIG. 9 and FIG. 10 are the same as FIG. 7 and FIG. 8, respectively, and illustrate an example embodiment of a pre-stubbed configuration of the multi-port accumulator and tail cable;

FIG. 11 is a schematic diagram of an example embodiment of an RoF wireless picocellular system according to the present invention similar to that shown in FIG. 1 but that utilizes a number of multi-port accumulators;

FIG. 12 is a close-up plan view of one of the multi-port accumulators of FIG. 11, showing the associated picocellular coverage area as made up of four picocellular coverage sub-areas associated with the four transponders supported by the multi-port accumulator;

FIG. 13 is an example embodiment of a transponder for use with the multi-port accumulator and that includes an antenna system with adjustable antenna directionality;

FIG. 14 is a schematic plan view of an example embodiment of a multi-port accumulator having a hexagonal-shaped housing that supports six transponders; and

FIG. 15 is a schematic plan view of an example embodiment of a multi-port accumulator having a triangular-shaped housing that supports three transponders.

DETAILED DESCRIPTION OF THE INVENTION

Reference is now made in detail to certain embodiments of the invention, examples of which are illustrated in the accompanying drawings. Whenever possible, the same or analogous reference numbers are used throughout the drawings to refer to the same or like parts.

Generalized Optical-Fiber-Based RoF Wireless Picocellular System

FIG. 1 is a schematic diagram of a generalized example embodiment of an optical-fiber-based RoF wireless picocellular system 10. System 10 includes a head-end unit 20, a distribution unit 26, at least one RoF transponder unit (“transponder”) 30, a primary optical fiber RF communication link 34 that optically couples the head-end unit to the distribution unit, and at least one secondary optical fiber RF communication link 36 that couples one or more transponders to the distribution unit, thus establishing a connection between the transponder(s) and the head-end unit. In an example embodiment, optical fiber RF communication links 34 and 36 include at least one optical fiber, and preferably two optical fibers (e.g., uplink and downlink optical fibers, as discussed below). As discussed in detail below, system 10 is adapted to form a picocell 40 substantially centered about transponder 30. One or more transponders 30 form a picocellular coverage area 44. Distribution unit 26 is adapted to divide the primary optical fiber RF communication link 34 into a number of secondary RF optical fiber communication links (hereinafter, “tail cables”) 36 that facilitate distributing a number of transponders 30 throughout a given infrastructure.

Head-end unit 20 is adapted to perform or to facilitate any one of a number of RoF applications, such as radio-frequency identification (RFID), wireless local-area network (WLAN) communication, or cellular phone service to provide non-limiting examples. Shown within picocell 40 is a client device 45 in the form of a computer. Client device 45 includes an antenna 46 (e.g., a wireless card) adapted to receive and/or send wireless electromagnetic RF signals.

FIG. 2 is a detailed schematic diagram of an example embodiment of head-end unit 20 of system 10 of FIG. 1. Head-end unit 20 includes a service unit 50 that provides electrical RF service signals for a particular wireless service or application. In an example embodiment, service unit 50 provides electrical RF service signals by passing (or conditioning and then passing) such signals from one or more outside networks 52. In a particular example embodiment, this includes providing WLAN signal distribution as specified in the IEEE 802.11 standard, i.e., in the frequency range from 2.4 to 2.5 GHz and from 5.0 to 6.0 GHz. In another example embodiment, service unit 50 provides electrical RF service signals by generating the signals directly. In another example embodiment, service unit 50 coordinates the delivery of the electrical RF service signals between client devices within picocellular coverage area 44.

Service unit 50 is electrically coupled to an electrical-to-optical (E/O) converter 60 that receives an electrical RF service signal from the service unit and converts it to a corresponding optical signal. In an example embodiment, E/O converter 60 includes a laser suitable for delivering sufficient dynamic range for the RF-over-fiber applications of the present invention, and optionally includes a laser driver/amplifier electrically coupled to the laser. Examples of suitable lasers for E/O converter 60 include laser diodes, distributed feedback (DFB) lasers, Fabry-Perot (FP) lasers, and vertical cavity surface emitting lasers (VCSELs).

Head-end unit 20 also includes an optical-to-electrical (O/E) converter 62 electrically coupled to service unit 50. O/E converter 62 receives an optical RF service signal and converts it to a corresponding electrical signal. In an example embodiment, O/E converter is a photodetector, or a photodetector electrically coupled to a linear amplifier. E/O converter 60 and O/E converter 62 constitute a “converter pair unit” 66.

In an example embodiment, service unit 50 includes an RF signal modulator/demodulator (M/D) unit 70 that generates an RF carrier of a given frequency and then modulates RF signals onto the carrier, and that also demodulates received RF signals. Service unit 50 also includes a digital signal processing unit (“digital signal processor”) 72, a central processing unit (CPU) 74 for processing data and otherwise performing logic and computing operations, and a memory unit 76 for storing data, such as RFID tag information or data to be transmitted over the WLAN. In an example embodiment, the different frequencies associated with the different signal channels are created by M/D unit 70 generating different RF carrier frequencies based on instructions from CPU 74. Also, as described below, the common frequencies associated with a particular combined picocell are created by M/D unit 70 generating the same RF carrier frequency.

FIG. 3 is a detailed schematic diagram of an example embodiment of the portion of system 10 of FIG. 1 that includes distribution unit 26 and transponder 30. Transponder 30 includes a converter pair 66, wherein the E/O converter 60 and the O/E converter 62 therein are electrically coupled to an antenna system 100 via an RF signal-directing element 106, such as a circulator. Signal-directing element 106 serves to direct the downlink and uplink electrical RF service signals, as discussed below. In an example embodiment, antenna system 100 includes one or more directional patch antennas, such as disclosed in U.S. patent application Ser. No. 11/504,999 filed Aug. 16, 2006, which patent application is incorporated herein by reference. In another example embodiment, antenna system has enhanced directionality, such as disclosed in U.S. patent application Ser. No. 11/703,016 filed Feb. 6, 2007, which patent application is incorporated by reference herein. Antenna system 100 is discussed in greater detail below. Transponder 30 also includes a housing 102 that in an example embodiment houses some or all of the various transponder elements. In an example embodiment, some or all of antenna system 100 lies outside of housing 102. In an example embodiment, housing 102 houses only the elements making up converter pair unit 66.

FIG. 4 is a close-up view of an alternative example embodiment for transponder 30 wherein antenna system 100 includes two antennae: a transmitting antenna 101T electrically coupled to O/E converter 62, and a receiving antenna 101R electrically coupled to E/O converter 60. The two-antenna embodiment obviates the need for RF signal-directing element 106. Note also that the example embodiment of transponder 30 in FIG. 3 includes DC power converter 180 within converter pair unit 66, and that antenna system 100 is within housing 102. FIG. 4 also illustrates an example embodiment wherein transponder 30 includes a connector 31 adapted to connect to a corresponding connector plug 37 on tail cable 36. FIG. 4 also illustrates an example embodiment that includes at least one antenna reflector 104 arranged relative to antenna system 100 so as to enhance the directionality of the antenna system, such as described in aforementioned U.S. patent application Ser. No. 11/703,016.

Transponders 30 of the present invention differ from the typical access point device associated with non-RoF wireless communication systems in that the preferred embodiment of the transponder has just a few signal-conditioning elements and no digital information processing capability. Rather, the information processing capability is located remotely in head-end unit 20, and in a particular example, in service unit 50. This allows transponder 30 to be very compact and virtually maintenance free. In addition, the preferred example embodiment of transponder 30 consumes very little power, is transparent to RF signals, and does not require a local power source, as described below.

With reference to FIG. 2 and FIG. 3, in an example embodiment, optical fiber RF communication link 34 and tail cable 36 includes at least one downlink optical fiber 136D and at least one uplink optical fiber 136U. Downlink and uplink optical fibers 136D and 136U in optical fiber RF communication link 34 optically couple converter pair 66 at head-end unit 20 to distribution unit 26, while the downlink and uplink optical fibers in tail cable 36 connect the distribution unit 26 to the converter pair at transponder 30. Thus, each transponder 30 is optically coupled to head-end unit 20.

In an example embodiment, the optical-fiber-based wireless picocellular system 10 of the present invention employs a known telecommunications wavelength, such as 850 nm, 1300 nm, or 1550 nm. In another example embodiment, system 10 employs other less common but suitable wavelengths such as 980 nm.

Example embodiments of system 10 include either single-mode optical fiber or multimode optical fiber for downlink and uplink optical fibers 136D and 136U. The particular type of optical fiber depends on the application of system 10. For many in-building deployment applications, maximum transmission distances typically do not exceed 300 meters. The maximum length for the intended RoF transmission needs to be taken into account when considering using multi-mode optical fibers for downlink and uplink optical fibers 136D and 136U. For example, it has been shown that a 1400 MHz.km multi-mode fiber bandwidth-distance product is sufficient for 5.2 GHz transmission up to 300 m.

In an example embodiment, the present invention employs 50 μm multi-mode optical fiber for the downlink and uplink optical fibers 136D and 136U, and E/O converters 60 that operate at 850 nm using commercially available VCSELs specified for 10 Gb/s data transmission. In a more specific example embodiment, OM3 50 μm multi-mode optical fiber is used for the downlink and uplink optical fibers 136D and 136U.

Wireless system 10 also includes a power supply 160 that generates an electrical power signal 162. Power supply 160 is electrically coupled to head-end unit 20 for powering the power-consuming elements therein. In an example embodiment, an electrical power line 168 runs through the head-end unit and through distribution unit 26 to each transponder 30 to power E/O converter 60 and O/E converter 62 in converter pair 66, the optional RF signal-directing element 106 (unless element 106 is a passive device such as a circulator), and any other power-consuming elements (not shown). Alternatively, electrical power line 168 runs from distribution unit 26 that also optionally includes a power supply 160 (FIG. 3). In an example embodiment, electrical power line 168 includes two wires 170 and 172 that carry a single voltage and that are electrically coupled to a DC power converter 180 at transponder 30. DC power converter 180 is electrically coupled to E/O converter 60 and O/E converter 62, and changes the voltage or levels of electrical power signal 162 to the power level(s) required by the power-consuming components in transponder 30. In an example embodiment, DC power converter 180 is either a DC/DC power converter, or an AC/DC power converter, depending on the type of power signal 162 carried by electrical power line 168. In an example embodiment, electrical power line 168 includes standard electrical-power-carrying electrical wire(s), such as a twisted copper pair (e.g., 18-26 AWG (American Wire Gauge)) used in standard telecommunications and other applications. In another example embodiment, electrical power line 168 (dashed line) runs directly from power supply 160 to transponder 30 rather than from or through head-end unit 20. In another example embodiment, electrical power line 168 includes more than two wires and carries multiple voltages.

In an example embodiment, head-end unit 20 is operably coupled to an outside network 52 via a network link 53 (FIG. 2).

Multi-Port Accumulator

As mentioned above, a RoF wireless picocellular system that employs a linear array of transponders has some shortcomings relating to its manufacture and deployment. Accordingly, an aspect of the present invention addresses these and other shortcomings by consolidating transponders 30 into a more compact and more easily manufacturable and deployable RoF wireless picocellular system.

FIG. 5 is a schematic perspective diagram of an example embodiment of a multi-port accumulator apparatus 200 (“multi-port accumulator”) according to the present invention. Multi-port accumulator 200 includes a housing 202 having a number of sidewalls 204, a top wall 206 and a bottom wall 208. Housing 202 includes two or more transponder connector ports 212 formed in corresponding two or more of sidewalls 204. Multi-port accumulator 200 of FIG. 5 illustrates an example embodiment of a rectangular (square) housing 202 having four sidewalls 204A, 204B, 204C and 204D with four associated RoF transponder connector ports (“transponder ports”) 212A, 212B, 212C and 212D. Housing 202 also includes a tail cable port 214 on top wall 206. Housing 202 can generally be made of a number of suitable materials, such as metal or plastic.

FIG. 6 is a plan view of multi-port accumulator 200 with top wall 206 removed, showing tail cable connector port (“tail cable port”) 214 and four transponders 30A, 30B, 30C and 30D operably coupled to the device via associated transponder ports 212A, 212B, 212C and 212D. Device 200 includes, for each transponder port 212, optical fiber sections 236U and 236D that correspond to uplink and downlink optical fibers 136U and 136D in tail cable 36. Thus, each optical fiber section 236UA and 236DA is optically connected at one end to transponder port 212A and at its opposite end to tail cable port 214, etc.

Likewise, device 200 includes for each transponder port 212 an electrical power line section 268 connected at one end to the transponder port and at its opposite end to tail cable port 214. Thus, electrical power line section 268A electrically connects transponder port 212A to tail cable port 214, etc.

FIG. 7 is a side view of the multi-port accumulator 200 of FIG. 6. showing the connection of tail cable 36 to the multi-port accumulator using tail cable connector plug 37 connected to tail cable port 214. FIG. 8 is a side view of device 200 as shown in FIG. 7 with sidewall 204B removed, illustrating the optical and electrical connections between tail cable port 214 and transponder port 212C via optical fiber sections 236UC, 236DC and electrical power line section 168C. The other transponder ports 212A, 212B and 212C are similarly connected to tail cable port 214.

FIG. 9 and FIG. 10 are similar to FIG. 7 and FIG. 8, respectively, and illustrate an example embodiment of multi-port accumulator 200 and tail cable 36 in a pre-stubbed configuration that does not require tail cable port 214. In the pre-stubbed configuration embodiment, rather than using separate optical fiber sections 236U and 236D to connect to each RF transponder port 212, uplink and downlink optical fibers 136U and 136D are stripped out of the tail cable and connected directly to associated RF transponder ports.

In an example embodiment, tail cable 36 includes a connector plug 37 at the end opposite multi-port accumulator 200 for connecting to distribution unit 26 at a mating connector socket 27 (FIG. 3). Similarly, further embodiments of the present invention comprise tail cables, similar to tale cable 36, that include a connector plug, similar to the connector plug 37, rather than cable ports, such as cable ports 212A-212D, to connect the transponders, such as transponders 30. Even further embodiments of the present invention include multi-port accumulators with permanently mounted cable assemblies to which transponders are permanently connected.

General Method of Operation Using Multi-Port Accumulator

FIG. 11 is a schematic diagram of an example embodiment of an RoF wireless picocellular system 10 similar to that shown in FIG. 1 but that utilizes one or more multi-port accumulators 200 according to the present invention to deploy transponders 30. Note that the lower-most multi-port accumulator in FIG. 11 is in the aforementioned pre-stubbed configuration discussed in connection with FIG. 9 and FIG. 10.

With reference to FIG. 11 as well as to FIG. 2, in the operation of system 10 service unit 50 in head-end unit 20 generates an electrical downlink RF service signal SD (“electrical signal SD”) corresponding to its particular application. In an example embodiment, this is accomplished by digital signal processor 72 providing RF M/D unit 70 with an electrical signal (not shown) that is modulated onto an RF carrier to generate a desired electrical signal SD.

Electrical signal SD is received by E/O converter 60, which converts this electrical signal into a corresponding optical downlink RF signal SD′ (“optical signal SD′”), which is then directed to a number (e.g., five) of downlink optical fibers 134D of primary optical fiber RF communication link 34. It is noted here that in an example embodiment optical signal SD′ is tailored to have a given modulation index. Further, in an example embodiment the modulation power of E/O converter 60 is controlled (e.g., by one or more gain-control amplifiers, not shown) to vary the transmission power from antenna system 100. In an example embodiment, the amount of power provided to antenna system 100 is varied to define the size of picocell coverage area 44 of the associated picocell 40.

Optical signal SD′ travels over downlink optical fibers 134D to distribution unit 26, which serves to direct signals SD′ to the downlink optical fibers 136D of the five tail cables 36. Optical signal SD′ then travels over the respective tail cables 36 to the associated multi-port accumulator 200. Optical signals SD′ in each downlink optical fiber 136D are then directed to the associated downlink optical fiber section 236D via tail cable port 214 and thus to the associated transponder connector port 212. Each optical signal SD′ is then received by O/E converter 62 in the associated transponder 30. Each O/E converter 62 converts optical signal SD′ back into electrical signal SD, which then travels to signal-directing element 106. Signal-directing element 106 then directs electrical signal SD to antenna system 100. Electrical signal SD is fed to antenna system 100, causing it to radiate a corresponding electromagnetic downlink RF signal SD″ (“electromagnetic signal SD″”) to create an associated picocellular coverage area.

FIG. 12 is a close-up plan view of one of the multi-port accumulators 200 of FIG. 11, showing the picocellular coverage area 44 associated with the multi-port accumulator. Because antenna system 100 of each transponder 30 supported by multi-port accumulator 200 is directional, picocellular coverage area 44 is made up of two or more sub-areas 44A, 44B, . . . etc.—such as sub-areas 44A, 44B, 44C and 44D as shown in FIG. 12. If a client device 45 is within one of the picocellular coverage sub-areas (e.g., sub-area 44A as shown in FIG. 12), the client device will receive electromagnetic signal SD″ via client device antenna 46 (FIG. 1), which may be part of a wireless card, or a cell phone antenna, for example. Antenna 46 converts electromagnetic signal SD″ into electrical signal SD in the client device (signal SD is not shown therein). Client device 45 then processes electrical signal SD, e.g., stores the signal information in memory, displays the information as an e-mail or text message, etc.

In an example embodiment, client device 45 generates an electrical uplink RF signal SU (not shown in the client device), which is converted into an electromagnetic uplink RF signal SU″ (“electromagnetic signal SU″”) by antenna 46.

Because client device 45 is located within picocellular coverage sub-area 44A, electromagnetic signal SU″ is detected by antenna system 100 of the transponder 30A. Antenna system 100 converts electromagnetic signal SU″ back into electrical signal SU. Electrical signal SU is directed by signal-directing element 106 to E/O converter 60, which converts this electrical signal into a corresponding optical uplink RF signal SU′ (“optical signal SU′”), which is then directed into uplink optical fiber section 236U at transponder port 212A. Optical signal SU′ travels over optical fiber section 236U to tail cable port 214, which serves to direct this optical signal onto the associated uplink optical fiber 136U of the associated tail cable 36 connected to the tail cable port.

Optical signal SU′ travels over uplink optical fiber 136U to distribution unit 26, where it is directed to the associated uplink optical fiber 134U of primary RF optical fiber communication link 134. Optical signal SU′ then travels over primary RF optical fiber communication link 134 to head-end unit 20, where it is received by O/E converter 62. O/E converter 62 converts optical signal SU′ back into electrical signal SU, which is then directed to service unit 50. Service unit 50 receives and processes signal SU, which in an example embodiment includes one or more of the following: storing the signal information; digitally processing or conditioning the signal; sending the signal on to one or more outside networks 52 via network links 224; and sending the signal to one or more client devices 45 in one or more of the other picocellular coverage areas 44 or sub-areas 44A, 44B, etc. In an example embodiment, the processing of signal SU includes demodulating this electrical signal in RF signal M/D unit 70, and then processing the demodulated signal in digital signal processor 72.

Transponder with Adjustable Antenna System Directivity

FIG. 13 is an example embodiment of transponder 30 that includes an antenna system 100 that has adjustable directivity. Transponder 30 of FIG. 13 includes two or more antenna elements 101 such as the three antenna elements 101A, 101B and 101C shown, each having a different directivity (i.e., EM radiation pattern). Antenna elements 101 are electrically connected to an antenna switch 300 that switches among the antenna element(s) 101 of antenna system 100 to be used.

In an example embodiment, antenna element 101A is configured to provide coverage for all or substantially all of picocell coverage area 44, antenna element 101B is configured to cover two picocell coverage sub-areas (say, sub-areas 44A and 44B), while antenna element 101C is configured to cover picocell coverage sub-area 44A. This allows for multi-port accumulator 200 to form some or all of picocell coverage area 44 using one, some or all of transponders 30 of multi-port accumulator 200. In an example embodiment, antenna switch 300 includes an antenna 302 and is configured to be switchable via a wireless switching signal SS received by antenna 302. In another example embodiment, switching signal SS is non-wireless and originates from head-end unit 20 or from distribution unit 26.

Other Multi-Port Accumulator Housing Geometries

For the sake of illustration, multi-port accumulator 200 is described above in connection with a rectangular-shaped housing 202 that supports four transponders 30. FIG. 14 is a schematic plan view of an example embodiment of a multi-port accumulator 200 having a hexagonal-shaped that operably supports six transponders 30. Likewise, FIG. 15 is a schematic plan view of an example embodiment of a multi-port accumulator 200 having a triangular-shaped housing that operably supports three transponders 30. Further embodiments of the present invention include alternative accumulators comprising any number of transponders in any geometric arrangement.

It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. 

1. A multi-port accumulator apparatus for operably supporting two or more radio-over-fiber (RoF) transponders and for providing a connection to a tail cable that carries uplink and downlink optical signals and electrical power, comprising: a housing; two or more RoF transponder ports supported by the housing, with each RoF transponder port configured to operably connect to one of the RoF transponders; a tail cable port supported by the housing and configured to operably connect to the tail cable, the tail cable port being optically and electrically connected to each RoF transponder port so as to provide the uplink and downlink optical signals and the electrical power to each RoF transponder.
 2. The apparatus of claim 1, wherein: the tail cable port is adapted to receive two or more external pairs of uplink and downlink optical fibers carried by the tail cable; the tail cable port is optically coupled to the two or more RoF transponder ports via respective two or more internal pairs of uplink and downlink optical fiber sections; and the tail cable port is configured to optically couple the external pairs of uplink and downlink optical fibers to the internal pairs of uplink and downlink optical fibers.
 3. The apparatus of claim 2, wherein: the tail cable port is adapted to receive an external electrical power line carried by the tail cable and that carries the electrical power; the tail cable port is electrically coupled to the two or more RoF transponder ports via respective two or more internal electrical power line sections; and the tail cable port is configured to electrically couple the external electrical power line to the two or more internal electrical power line sections so as to provide electrical power to each of the RoF transponders.
 4. The apparatus of claim 1, wherein the housing has four sidewalls and four RoF transponder ports, with one transponder port supported by each sidewall.
 5. The apparatus of claim 1, wherein the apparatus has associated therewith a picocell coverage area made up of two or more picocell coverage sub-areas respectively formed by the two or more RoF transponders.
 6. The apparatus of claim 1, wherein at least one of the RoF transponders includes an antenna system having an adjustable antenna directivity.
 7. The apparatus of claim 1, wherein at least one of the RoF transponders includes a patch antenna.
 8. An RoF wireless picocellular system, comprising: two or more multi-port accumulator apparatuses according to claim 1, with each multi-port accumulator apparatus optically coupled to a corresponding one of the tail cables.
 9. The RoF wireless picocellular system of claim 8, further including: a head-end unit configured to generate downlink optical signals and to receive uplink optical signals; and a distribution unit optically coupled to the head-end unit and each tail cable so as to distribute the uplink and downlink optical signals between the transponders of each multi-port accumulator apparatus and the head-end unit.
 10. A method of forming a radio-over-fiber (RoF) wireless picocellular coverage area, comprising: operably supporting two or more RoF transponders on a housing; providing downlink optical signals for the two or more RoF transponders to a tail cable port on the housing via a tail cable; and distributing the downlink optical signals through the housing to one or more of the RoF transponders so that the one or more RoF transponders contribute to forming a picocellular coverage area.
 11. The method of claim 10, wherein each RoF transponder receives the downlink optical signals and forms a picocellular coverage sub-area that constitutes a portion of the picocellular coverage area.
 12. The method of claim 10, further including: operably supporting the two or more RoF transponders at RoF transponder ports that are optically and electrically coupled to the tail cable port.
 13. The method of claim 12, further including: carrying electrical power in the tail cable in an electrical power line; and distributing electrical power through the housing via electrical power line sections connected to the tail cable port and each of the RoF transponder ports so as to power each of the RoF transponders.
 14. The method of claim 10, wherein each RoF transponder includes an antenna system, and further including adjusting the directivity of at least one of the antenna systems to adjust the corresponding RoF transponder's contribution to the picocellular coverage area.
 15. A multi-port accumulator apparatus for supporting a plurality of RoF transponders for a radio-over-fiber (RoF) wireless picocellular system, comprising: a housing; a plurality of RoF transponder ports supported by the housing, with each RoF transponder port adapted to operably connect with one of the RoF transponders; a tail cable optically coupled within the housing to the plurality of RoF transponder ports so as to provide for optical transmission of uplink and downlink optical signals between the tail cable and the plurality of RoF transponder ports; and wherein the tail cable is electrically coupled within the housing to the plurality of RoF transponder ports so as to provide electrical power to each of the plurality of RoF transponder ports.
 16. The apparatus of claim 15, further including one RoF transponder operably connected to each RoF transponder port.
 17. The apparatus of claim 16, wherein each RoF transponder has a directional antenna system configured to form an associated picocellular coverage sub-area that makes up a picocellular coverage area formed by two or more of the RoF transponders.
 18. The apparatus of claim 15, further including: a tail cable port supported by the housing and optically and electrically coupled to each RoF transponder port; a tail cable plug operably fixed to the tail cable at a tail cable end; and wherein the tail cable is operably connected to the tail cable port via the tail cable plug.
 19. An RoF wireless picocellular system, comprising two or more of the apparatuses of claim
 18. 20. The apparatus of claim 18, wherein each RoF transponder port is optically coupled to the tail cable port via downlink and uplink optical fiber sections internal to the housing. 